Outdoor space is increasingly becoming part of the everyday living environment. Sales in outdoor furniture are growing steadily – predicted to reach USD 1,600 million by the end of 2022. For manufacturers, this represents a significant business opportunity, if they can show their products are resistant to the negative effects of weathering.
At the same time as this increasing demand for outdoor furniture, it is predicted that Millennials, defined as aged between 20 and 35 in 2016, will become the dominant population group in the US in 2019, overtaking the Baby Boomers (52 -70). A recent Casual Living study showed Millennials favored muted colors (57% preference) and modern styles (six out of ten Millennial consumers). They were also more inclined to live in urban environments, requiring the necessity to create multipurpose areas with convertible furniture. The survey also showed they expected to use the furniture for between two to four years and over half would only buy a product if they had tried it.
Millennials are, therefore, discerning consumer who look for quality and durability when deciding on the acquisition of a piece of outdoor furniture. It must retain its strength, stability and aesthetics despite being exposed to environmental factors – temperature, sunlight and moisture.
To help manufacturers developed attractive and durable outdoor furniture, they should test their products using laboratory accelerated aging techniques to replicate weathering processes. These procedures use aggravated environmental factors to speed up the normal aging process, thereby helping manufacturers understand the long-term effects of exposure to environmental factors in shorter timeframes and under standardized laboratory conditions.
The effects can broadly be split into two forms:
- Changes in visual properties or aesthetic appeal – fading, yellowing, color change, gloss reduction
- Changes in physical properties – cracking, peeling, embrittlement, loss of tensile strength
It should be noted, visible alterations may also be symptomatic of changes to the physical properties of the product and could therefore become a safety issue.
The Sun is the primary driver in altering the visual appearance of furniture, with heat and moisture acting as catalysts. Obviously, the outdoor natural exposure method is the most straightforward form of exposure, if time permits. The problem with this is the variability of climate at different sites means test data would only truly be applicable to the test site. Using weatherometers to accelerate sunlight degradation in the controlled environment of a laboratory is a far more sensible approach, providing greater consistency in the results.
Heat and light oxidation, (also known as photooxidation), in pigments, binding agents and other coating additives – cause molecular chains in the product to break down, resulting in embrittlement and visual changes.
The two primary laboratory practices used to replicate harmful effects of sunlight are:
- Fluorescent Ultraviolet, using ASTM G154 – Standard Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials
- Xenon Arc, using ASTM G155 – Standard Practice for Operating Xenon Arc Light Apparatus for Exposure of Non-Metallic Materials
These simulate sunlight alongside heat and moisture, but the primary difference is the sun’s wavelength they replicate:
- Xenon Arc - full spectrum sunlight and is therefore a closer replication of outdoor sun exposure
- UV chamber - sunlight’s UV band. Fluorescent UVA and UVB lamps replicate 300 – 400 nm wavelengths – where most physical damage occurs
These approaches allow manufacturers to test different facets of the aging process: Xenon Arc is best for evaluating color change of outdoor pigments and dye over time; QUV to test for embrittlement and physical change, especially in polymers and durable outdoor coatings.
It is also importance to test for resistance to extreme of temperature. To evaluate this, manufacturers can use industry methods but often their application is made redundant by the incorporation of elevated temperature tests in other aging methods.
Methods for testing include:
- ASTM D1211 – Heat and Cold Resistance
- ASTM D2247 – Head and Humidity Resistance
- ASTM C666 – Rapid Freeze and Thaw of Concrete
Another major effect of weathering is corrosion – the gradual degradation of refined materials, usually metals, into a more stable form. It occurs naturally through chemical and/or electrochemical reaction but can be accelerated using laboratory practices:
- ASTM International’s ASTM B117 – Standard Practice for Operating Salt Spray (Fog) Apparatus services as the principal corrosion testing guidance document.
- ASTM B117 creates a controlled corrosive environment using a 5% salt solution that is atomized into a “salt fog”. Samples are left in this environment for pre-determined amounts of time, or until a failure is identified.
In addition, ASTM D5894 – Standard Practice for Cyclic Salt Fog/UV Exposure of Painted Metal uses both UV and corrosion chambers to more closely simulate outdoor exposure. There is evidence that exposure to one element will affect the way a product reacts to other weathering agents. Materials are therefore exposed to alternating periods of UV and salt fog exposure.
There are, of course, limitations to these processes:
- Space: limited space in chambers means often only material samples are tested; the full complexity of a product and how each material may affect the other constituent parts is not
- Correlation: no agreed upon correlation between testing time and length of environmental exposure – e.g. some authorities say 1,000 hours of ASTM G154 UV equates to a year in Florida, but others think it’s double
- Singular Replication: methods only recreate one environment, but real-life climates can vary drastically – e.g. Arizona is hot and dry, Maine is wet, and Florida is both hot and wet
One way to address these limitations is to design a proper weather evaluation. To do this, it is critical to review the following factors:
- Objective: to ascertain how a piece of outdoor furniture will perform in its intended use environment. Because fool proof correlation of laboratory and real-life exposure does not exist, it is advised to corroborate test results with real-life observations in the field. These methods also allow comparison between materials – useful for material selection
- Product Construction: material composition and construction are critical as materials react differently when exposed to varying types of exposures, e.g. concrete and stone can withstand sunlight, but are susceptible to cracking through water absorption and freezing temperatures
- Primary Intended Use Environment: replicating the most severe use environments will limit a study’s lead time, cost, and sample requirements
- Criteria: quantitative criteria are needed with results that can be used as a basis for evaluation and subsequent decision
It is then important to evaluate the results. Ideally, once a product has been ‘aged’ it should then be re-evaluated for loading, stability, and leg durability, but limitations of chamber size mean often only components and materials have been tested.
Weathering practices typically do not specify evaluation procedures. Instead, guidance must come from specific component and/or attribute methods.
Once criteria have been identified they will be used to evaluate the product in the “as received” state. It is critical to establish this “as received” benchmark as the tests will be repeated afterward to ascertain changes as a result of the exposure.
Common visual evaluation methods include:
- Color: ASTM D2244 – Standard Test Method for Calculation of Color Differences from Instrumentally Measured Color Coordinates – a spectrophotometer is used to measure the samples color before and after the test
- Gloss: ASTM D523 – Standard Test Method for Specular Gloss – identifies gloss change
- Surface Corrosion: Standard Test Method for Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments – includes procedures to evaluate subsurface corrosion, surface corrosion, edge corrosion, and corrosion of non-uniform areas
Numerous evaluation methods exist that focus on physical changes:
- Paint adhesion – ASTM D3359 Standard Test Methods for Measuring Adhesion by Tape Test
- Elongation and Tensile Strength – ASTM D2370 Standard Test Method for Tensile Properties of Organic Coatings
- Flexibility – ASTM D522 Standard Test Methods for Mandrel Bend Test of Attached Organic Coatings
- Abrasion Resistance – ASTM D4060 Taber Abrasion
- Moisture Content – Primarily used for wood, a moisture meter can quantify changes in product’s moisture content, which can lead to warping or cracking
ASTM has also created specific standards for testing outdoor plastic furniture,:
- ASTM F1561 Standard Performance Requirements for Plastic Chairs for Outdoor Use
- ASTM F1838 Standard Performance Requirements for Child's Plastic Chairs for Outdoor Use
- ASTM F1858 Standard Performance Requirements for Multipositional Plastic Chairs with Adjustable Backs or Reclining Mechanisms for Outdoor Use
- ASTM F1988 Standard Performance Requirements for Plastic Chaise Lounges, With or Without Moving Arms, With Adjustable Backs, for Outdoor Use
The increasing demand for outdoor furniture means manufacturers need to be sure they are producing furniture that conforms to the expectations of consumers. SGS has considerable experience in offering efficient and cost-effective testing solutions for outdoor furniture to help manufacturers bring quality, durable products to their target markets.
To learn more about SGSTesting.
For more information, please contact:
Senior Technical Manager - Hardlines
SGS - North America, Inc.
Tel: +1 973 461 1505
SGS is the world’s leading inspection, verification, testing and certification company. SGS is recognized as the global benchmark for quality and integrity. With more than 95,000 employees, SGS operates a network of over 2,400 offices and laboratories around the world.